49ers DE Drake Jackson won’t complete his rehab before camp ends

49ers defensive end Drake Jackson will not return during training camp, coach Kyle Shanahan said Monday.Jackson began camp on the active/physically unable to perform list after undergoing patellar tendon surgery. Shanahan said he does not have a timeline for Jackson to return."We've got to see how rehab continues to go but definitely not any time in camp," Shanahan said, via 49erswebzone.com. "Anytime you do that type of surgery that he had . . . those are big surgeries. They're tough to come back from. You never know how they're going to react. We always know it's a possibility to take a long time, and it's taking a long time."Shanahan also said offensive lineman Spencer Burford will see another doctor before determining whether to undergo surgery on his broken right hand.Wide receiver Jacob Cowing (hamstring), running back Isaac Guerendo (hamstring) and wide receiver Tay Martin (hamstring) did not practice Monday. Guerendo could miss a "few weeks," but Cowing and Martin should return next week.